All the world’s cultures have a conception of time, but in only half the world’s languages is the ordering of events expressed in the form of tense (Pinker, p. 189). The English language, for example, expresses conceptions of time with tenses but also in other ways, such as with adverbial time phrases such as “now,” “tomorrow” and “twenty-three days ago.” Philosophers have asked what we are basically committed to when we locate an event in the past, in the present, or in the future. For example, how should we understand the past tense verb in, “Mohammed’s birth occurred centuries ago”? There are two major answers. One answer is that tense distinctions represent objective features of reality that are not captured by the popular block universe approach. This answer takes tenses very seriously and is called the tensed theory of time, or the A-theory in McTaggart’s sense of A vs. B. A second answer to the question of the significance of tenses is that they are subjective features of the perspective from which the subject views the universe. Actually this disagreement isn’t really about tenses in the grammatical sense, but about the significance of the distinctions of past, present, and future which those tenses are used to mark.

On the tenseless theory of time, or the B-theory, whether the birth of Mohammed occurred there depends on the speaker’s perspective; similarly, whether the birth occurs then is equally subjective. The proponent of the tenseless view does not deny the importance or coherence of talk about the past, but will say it really is (or should be analyzed as being) talk about our own relation to events. My assertion that Mohammed’s birth has occurred might be analyzed as asserting that the birth event happens before the event of my writing this sentence.

This controversy is often presented as a dispute about whether tensed facts exist, with advocates of the tenseless theory objecting to tensed facts such as the fact of Mohammed’s having been born. The primary function of tensed facts is to make tensed sentences true. For the purposes of explaining that point, let us uncritically accept the Correspondence Theory of Truth and apply it to the following past tense sentence:

Custer died in Montana.
If we apply the Correspondence Theory directly to this sentence, then the tensed theory would imply

The sentence “Custer died in Montana” is true because it corresponds to the tensed fact that Custer died in Montana.
Opponents of tensed facts argue that the Correspondence Theory should be applied only indirectly. One approach, the classical tenseless approach, argues that the Correspondence Theory should be applied only to the result of analyzing away tensed sentences into equivalent sentences that do not use tenses. They might say that the sentence “Custer died in Montana” has this equivalent “eternal” sentence:

There is a time t such that Custer dies in Montana at time t, and time t is before the time of the writing of the sentence “Custer died in Montana” by Dowden in the article “Time” in The Internet Encyclopedia of Philosophy.
In this analysis, the verb dies is logically tenseless (although grammatically it is present tensed). Applying the Correspondence Theory to this new sentence yields:

The sentence “Custer died in Montana” is true because it corresponds to the tenseless fact that there is a time t such that Custer dies in Montana at time t, and time t is before the time of the utterance (or writing) of the sentence “Custer died in Montana” by Dowden in the article “Time” in The Internet Encyclopedia of Philosophy.
This analysis does not require tensed facts. The analysis is challenged on the grounds that it can succeed only for utterances or inscriptions, but a sentence can be true even if never uttered or written by anyone.

There are other challenges. Roderick Chisholm and A. N. Prior claim that the word “is” in the sentence “It is now midnight” is essentially present tensed because there is no translation using only tenseless verbs. Trying to analyze it as, say, “There is a time t such that t = midnight” is to miss the essential reference to the present in the original sentence because the original sentence is not always true, but the sentence “There is a time t such that t = midnight” is always true. So, the tenseless analysis fails. There is no escape by adding “and t is now” because this last indexical still needs analysis, and we are starting a vicious regress.

Earlier, Prior [1959] had argued that after a painful event,

one says, e.g., “Thank goodness that’s over,” and [this]…says something which it is impossible that any use of a tenseless copula with a date should convey. It certainly doesn’t mean the same as, e.g., “Thank goodness the date of the conclusion of that thing is Friday, June 15, 1954,” even if it be said then. (Nor, for that matter, does it mean “Thank goodness the conclusion of that thing is contemporaneous with this utterance.” Why should anyone thank goodness for that?).
D. H. Mellor, who advocates a newer subjective theory of tenses, says the truth conditions of any tensed sentence can be explained without tensed facts even if Chisholm and Prior are correct that some tensed sentences can not be translated into tenseless ones. If I am speaking to you and say, “It is now midnight,” then the conditions under which this is true are that my utterance of “It is now midnight” occurs at the same time as your hearing the utterance, which in turn is the same time as when our standard clock declares the time to be midnight in our reference frame. Notice that no tensed facts were appealed to in the explanation of those truth conditions. Mellor would say it is not the pastness of the painful event that explains why I say, “Thank goodness that’s over.” My gladness is explained by my belief that the event is past, plus its being true that the time of the occurrence of that utterance is greater than the time of the occurrence of the painful event. In addition, tenseless sentences can be used to explain the logical relations between tensed sentences: that one tensed sentence implies another, is inconsistent with yet another, and so forth. And understanding truth conditions and truth implications is the main thing you know when you understand a declarative sentence. In other words, the meaning of tensed sentences can be explained without utilizing tensed properties or tensed facts. Then Ockham’s Razor is applied. If we can do without essentially-tensed facts, then we should say essentially-tensed facts do not exist. To summarize, tensed facts were presumed to be needed to account for the truth of tensed talk; but the analysis shows that ordinary tenseless facts are adequate. So, there are no essentially-tensed facts, according to Mellor.